WO2023091062A1

WO2023091062A1 - A fluid treatment system with an uv lamp in a reactor

Info

Publication number: WO2023091062A1
Application number: PCT/SE2022/051055
Authority: WO
Inventors: Ulf Arbeus
Original assignee: Wallenius Water Innovation Ab
Priority date: 2021-11-17
Filing date: 2022-11-11
Publication date: 2023-05-25
Also published as: SE544918C2; SE2151400A1

Abstract

A fluid treatment system (2) comprising at least one ultra-violet, UV, light treatment lamp (6) arranged within an elongated protective UV-transparent sleeve (8) provided along a central longitudinal axis A, and a reactor (12) configured to receive said sleeve (8), whereby a fluid treatment chamber (4) for receiving fluid to be treated, is provided between an inner surface (14) of the reactor (12) and an outer surface (10) of the sleeve (8), wherein said reactor (12) extends along the axis A, between a first end (12a) and a second end (12b) of the reactor and wherein said treatment chamber (4) comprises an inlet (5a) for receiving fluid to be treated inside the treatment chamber (4) and an outlet (5b) for expelling treated fluid out from the treatment chamber (4), whereby the inlet (5a) is positioned such that fluid is introduced into the treatment chamber (4) from the first end (12a) of the reactor (12) and the outlet (5b) is provided closer to the first end (12a) than to the second end (12b) of the reactor (12), and wherein the inlet (5a) is provided closer to the sleeve (8) than the outlet (5b) is, wherein the treatment chamber (4) is one single open treatment chamber (4) which is surrounding the sleeve (8).

Description

A FLUID TREATMENT SYSTEM WITH AN UV LAMP IN A REACTOR

Technical field

The present disclosure relates to a fluid treatment system for treating a fluid by applying ultra-violet (UV) radiation to the fluid to be treated according to the preamble of the independent claim.

Background

There are many applications where UV light sources are used for treating fluids, such as gases and liquids. Wallenius Water Innovation AB in Sweden has developed and is selling water treatment equipment having a water purifier comprising an elongated tubular treatment chamber with an inlet and an outlet. In the centre of the treatment chamber a generally tubular quartz glass is arranged and inside the quartz glass is a UV source arranged, such as a lamp capable of generating wavelengths in the UV region.

One type of UV-light treatment reactor comprises an elongated UV-lamp arranged within a protective sleeve and provided with a circumferential channel outside the sleeve where the fluid is intended to flow. In the channel the fluid closest to the sleeve will receive the highest dose. And consequently the fluid farther out from the sleeve will receive a lower dose. The treatment chamber may be considered to have different dose intensity zones. Closest to the UV-lamp is the dose intensity zone having the highest UV-light dose.

Micro-organisms are inactivated by UV light as a result of damage to nucleic acids. The high energy associated with short wavelength UV energy, primarily around 260 nm, is absorbed by cellular RNA and DNA. This absorption of UV energy forms new bonds between adjacent nucleotides, creating double bonds or dimers. Dimerization of adjacent molecules, particularly thymine, is the most common photochemical damage. Formation of numerous thymine dimers in the DNA of bacteria and viruses prevents replication and their ability to infect.

The germicidal effects of UV are directly related to the dose of UV energy absorbed by a micro-organism. The UV dose is the product of the UV intensity and the time that a micro-organism is exposed to UV light (often referred to as residence time). The required disinfection limit or log-reduction will dictate the required UV dose. UV dose is typically expressed in mJ/cm², J/m² or pWs/cm² The exposure time of the UV system is determined by the reactor design and the flow rate of the water. The intensity is affected by the equipment parameters (such as lamp type, lamp arrangement, etc.) and water quality parameters (such as UV transmittance, etc.). Unlike chemical disinfectants, UV disinfection is not affected by the temperature, turbidity or pH of the water.

The UV dose response of a micro-organism is a measurement of its sensitivity to UV light and is unique to each micro-organism. A UV dose response curve is determined by irradiating water samples containing the micro-organism with various UV doses and measuring the concentration of viable infectious micro-organisms before and after exposure. The resultant dose response curve is a plot of the log inactivation of the organism versus the applied UV dose rate. 1-log inactivation corresponds to a 90% reduction; 2-log to a 99% reduction; 3-log to a 99.9% reduction and so on.

Thus, in order to achieve effective performance with regard to deactivation of microorganisms, the reactor has to be designed to ascertain that also the fluid farther away from the UV-lamp receives the required dose, which may be achieved by increasing the UV radiation. However, this has a negative impact of the energy consumption of the UV-lamp, which will be high.

In the following some exemplary prior art will be discussed, that disclose various related aspects, and specifically devices where various types of mixing of the fluid is provided.

US6224759 relates to a UV system comprising UV lamp units intended to radiate UV- light to a liquid. By arranging ring-shaped devices, e.g. washers, on each lamp unit the turbulent mixing of the liquid is increased.

US6420715 relates to a method and an apparatus for improved mixing in fluids in a UV- light treatment system. The apparatus includes means, e.g. delta wings, specially shaped baffles, propellers or contoured flow tubes, for inducing vortices in the fluid flow through UV-light treatment system. US7385204 relates to a fluid treatment device configured to treat a fluid with UV light. The device comprises a modular assembly including at least one baffle, e.g. a set of two baffles. The lamp geometry and baffles act as a baffling mechanism to direct the flow of fluid so as to increase uniformity in dose distribution by causing the fluid to flow into a volume where it will receive uniform treatment.

US8696192 relates to an apparatus comprising non-planar baffles included in the flow such that a flow is permitted to pass the baffle in a gap between the inner peripheral edge and the outer surface of the UV-transparent inner tube. Thereby vortices are induced in the liquid flow with the intention to increase efficiency in UV-light treatment.

In US2011/0318237 is disclosed a UV reactor comprising a baffle having a helical shape to provide for radial mixing of liquid. In another variation segmented baffles are provided to achieve helical mixing.

And finally, US2013/0153514 relates to an apparatus for treating fluids using ultraviolet light. The disclosure is in particular directed to a treatment chamber having an elliptical cross-sectional shape, but also mixing aspects are discussed. A mixing device is provided within a UV-transmissive conduit comprising fixed or rotating fins in order to facilitate uniform rotational mixing throughout the length of the conduit, and thereby enhancing dosage uniformity.

Thus, the intention in many of the solutions presented herein is to achieve more optimal geometry and flow conditions in relation to the distribution of UV light in the reactor chamber. Various means are presented to achieve this object, e.g. “open solutions” are applied, i.e. where means, e.g. wings, are arranged to control the formation of helixshaped fluid flows within a fluid enclosure.

Important aspects of UV-light treatment are effectiveness and energy efficiency. For specified flow, lamp emission power, UV absorbance of the fluid and UV dose response of the actual microorganism, the measured reduction of live organisms (CFU/mL) reflects the effectiveness of a UV reactor. A general challenge in UV reactor design is to achieve an even distribution of the inactivation performance. Efficiency is generally harmed by poor UV treatment distant from the lamp, typically close to the reactor wall.

Summary

The object of the present invention is to provide an improved fluid treatment system which efficiently reduces bacteria and other microorganisms in the fluid to be treated.

This is achieved by the present invention according to the independent claim.

According to the invention a fluid treatment system is provided comprising: at least one ultra-violet, UV, light treatment lamp arranged within an elongated protective UV-transparent sleeve provided along a central longitudinal axis A, said sleeve having an outer surface and an essentially circular cross-sectional shape; and a reactor configured to receive said sleeve, whereby a fluid treatment chamber for receiving fluid to be treated, is provided between an inner surface of the reactor and the outer surface of the sleeve; wherein said reactor extends along the axis A, between a first end and a second end of the reactor and wherein said treatment chamber comprises an inlet for receiving fluid to be treated inside the treatment chamber and an outlet for expelling treated fluid out from the treatment chamber, whereby the inlet is positioned such that fluid is introduced into the treatment chamber from the first end of the reactor and the outlet is provided closer to the first end than to the second end of the reactor, and wherein the inlet is provided closer to the sleeve than the outlet is, wherein the treatment chamber is one single open treatment chamber which is surrounding the sleeve.

Hereby, thanks to the design of the treatment chamber with both inlet and outlet provided in the same end of the reactor and with one single open treatment chamber, the fluid is allowed to flow in both directions along the UV-lamp without any internal separating walls inside the treatment chamber and an efficient UV treatment is achieved. Thanks to a relatively wide treatment chamber, i.e. a relatively large radius of the reactor which is surrounding the UV-lamp, a reversed flow of the fluid is allowed within the treatment chamber towards the outlet which is provided in the same end of the reactor as the inlet. Furthermore, the inlet is provided closer to the sleeve than the outlet is, i.e. a distance between the inlet and the sleeve is smaller than a distance between the outlet and the sleeve. Hereby an inlet flow of fluid to be treated will be provided close to the UV-lamp. The fluid is flowing from the inlet towards the second end of the reactor relatively close to the UV-lamp where the UV-light intensity is high. The fluid will be further treated in the reversed flow, but mostly at a larger distance from the UV-lamp. Hereby all the fluid will be efficiently treated.

Furthermore, in a fluid treatment system according to the invention there will be less problems caused by fouling and scaling on walls, thanks to the relatively large treatment chamber without any internal walls.

Hereby the UV light treatment system according to the invention has a design which will provide an efficient UV-light distribution for different fluids having a wide range of different UV-transmittance. This is because all fluid will first flow at a higher flow rate close to the UV-lamp where a high UV-intensity is provided and then the fluid will pass the UV-lamp a second time at a larger distance but at a lower flow rate whereby there is more time for further UV-treatment. In this design the reactor wall is positioned at a relatively large distance from the UV-lamp which will improve efficiency of the UV light treatment system thanks to a lower amount of UV-light being absorbed by the reactor wall compared to systems where the reactor wall is positioned closer to the UV-lamp. Hereby more UV-light is absorbed by the fluid and is hereby used for disinfection. Hereby an improved fluid treatment system is provided with regard to energy consumption.

In some systems a reactor wall is made from a reflective material in order to improve UV- treatment from reflection of UV-light from the reactor wall. However, such materials may be more expensive and may need cleaning. There is less need for the reactor wall to be reflective in the system according to the invention because the reactor wall is positioned at a larger distance from the UV-lamp. Furthermore, since there are no inner, UV- transparent, separating walls, separating the double directed flow, there is less need for cleaning of internal surfaces from fouling and scaling. Hereby maintenance is improved according to the invention.

A size of the inlet can be adapted such that the inlet flow rate of the fluid is higher than the reversed flow rate of the fluid. Hereby a fluid flow along the sleeve is assured. Thanks to the relatively high flow rate, also called a jet flow, of the fluid entering the treatment chamber the flows within the treatment chamber can be controlled in an optimal way, i.e. such that substantially all incoming fluid will be flowing along the sleeve from the first end to the second end of the reactor where the flow will be reversed and most of the reversed flow will take place at a larger distance from the sleeve than the incoming flow. This reversed flow will also have a lower flow rate due to the dimensions of the treatment chamber in relation to the size of the inlet. A higher inlet flow rate will also prevent any shortcut of flows, i.e. prevent that the inlet flow passes directly to the outlet. The flow rate of the flow coming from the inlet is higher than the flow rate of the flow towards the outlet. The high momentum of the inlet flow is recovered and generates a static pressure increase towards the second end. This pressure build-up supports a stable return flow towards the low-pressure side close to the inlet and outlet. With the solution according to the present invention, the jet flow closest to the lamp will reach the second end and prevent any short-cut between inlet and outlet.

Hereby reasons why the invention performs more efficiently than state-of-the art UV reactors are:

• The flow passes through the radiated volume twice between inlet and outlet.

• The flow passes through the radiated zone with the highest UV intensity closest to the lamp. Thanks to the high flow rate in the jet flow from the inlet towards the second end of the reactor there is also a strong turbulent mixing within this flow closest to the sleeve. Hereby all parts of the fluid will come closest to the sleeve where the UV intensity is highest and a good efficiency of UV treatment is achieved. The inlet flow passing through the treatment chamber, having the highest concentration of not yet inactivated microorganisms, will be passing through the radiated zone with the highest UV intensity of the treatment chamber.

In a fluid treatment system according to the invention the longitudinal flow in the high uv- intensity zone along and close to the uv-transparent sleeve, protecting the uv-lamp, is highly efficient compared to a perpendicular flow. A perpendicular flow is common practice in uv-reactors using medium pressure uv-lamps. Medium pressure lamps are many times more powerful per length compared to low pressure uv-lamps and often shorter and therefore commonly positioned perpendicular to the flow.

When a perpendicular flow is passing a sleeve, a flow stagnation area is formed in the wake down streams of the sleeve. A stagnation area in a high uv-intensity zone reduce the efficiency of the reactor. The main flow passing the reactor is, to a high degree, blocked from passing through that high uv-intensity zone.

Further embodiments are set forth in the dependent claims and in the detailed description.

Brief description of the drawings

Figure la shows schematically a perspective view of a fluid treatment system according to one embodiment of the invention.

Figure lb is a perspective view of one half of the same fluid treatment system as shown in Figure la.

Figure 1c is a cross section of the same fluid treatment system as shown in Figures la and lb.

Figure 2a is the same view as Figure 1c but with addition of an illustration of a fluid flow through the fluid treatment system.

Figure 2b is a CFD (Computational Fluid Dynamics) simulation of the flow pattern in a fluid treatment system according to one embodiment of the invention.

Figure 3 is a cross section of a fluid treatment system according to one embodiment of the invention. Detailed description

The fluid treatment system will now be described in detail with references to the appended figures. Throughout the figures the same, or similar, items have the same reference signs. Moreover, the items and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.

With references to figures 1-3, a fluid treatment system 2 is provided that is intended for treating a fluid with ultra-violet (UV) light. The fluid may be a gas or a liquid such as drinking water, waste water, ballast water, edible liquid, e.g. juices, but also cutting liquids.

In figure la a perspective view of a fluid treatment system 2 according to one embodiment of the invention is shown. In Figure lb a perspective view of one half of the same fluid treatment system 2 as shown in Figure la is shown and in Figure le a cross section of the same fluid treatment system 2 as shown in Figures la and lb is shown. Figure 2 is the same view as Figure 1c but with addition of an illustration of a fluid flow through the fluid treatment system 2. In Figure 3 another embodiment of a fluid treatment system 2 according to the invention is shown with a smaller change of geometry of the reactor 12 which will be further described below. With reference to all the drawings the invention is now described in more details.

The fluid treatment system 2 comprises at least one ultra-violet, UV, light treatment lamp 6 arranged within an elongated protective UV-transparent sleeve 8 provided along a central longitudinal axis A. The sleeve 8 has an outer surface 10 and an essentially circular cross-sectional shape. The fluid treatment system 2 comprises furthermore a reactor 12 configured to receive said sleeve 8, whereby a fluid treatment chamber 4 for receiving fluid to be treated, is provided between an inner surface 14 of the reactor 12 and the outer surface 10 of the sleeve 8. The inner surface 14 of the reactor 12 may have an essentially circular cross section and the fluid treatment chamber 4 may have an essentially annular cross section encircling the sleeve 8.

The reactor 12 extends along the axis A, between a first end 12a and a second end 12b of the reactor. The reactor comprises an outer surrounding wall 12c which has a substantially cylindrical form. The treatment chamber 4 comprises an inlet 5a for receiving fluid to be treated inside the treatment chamber 4 and an outlet 5b for expelling treated fluid out from the treatment chamber 4. The inlet 5a is positioned such that fluid is introduced into the treatment chamber 4 from the first end 12a of the reactor 12 and the outlet 5b is provided closer to the first end 12a than to the second end 12b of the reactor 12. In the embodiment as shown in Figures 1-3 the outlet 5b is positioned such that fluid is expelled out from the treatment chamber at the first end 12a of the reactor. In the embodiment as shown in Figures 1-3 both the inlet 5a and the outlet 5b are positioned at the first end 12a of the reactor 12. However, in other embodiments of the invention the outlet 5b can be positioned differently which will be further discussed below.

The inlet 5a is provided closer to the sleeve 8 than the outlet 5b is, i.e. a distance between the inlet 5a and the sleeve 8 is smaller than a distance between the outlet 5b and the sleeve 8. Hereby fluid which is introduced into the treatment chamber 4 via the inlet 5a will be flowing close along the sleeve 8 towards the second end 12b of the reactor 12. The treatment chamber 4 is one single open treatment chamber 4 which is surrounding the sleeve 8. Hereby, when a fluid is transferred as a flow of fluid through the fluid treatment system 2 for being treated, substantially all of the flow of the fluid will change direction at the second end 12b of the reactor. Hereby it will be a flow of fluid in both directions between the first and second ends 12a, b of the reactor 12 within the single open treatment chamber 4. Thanks to the inlet being provided at the first end 12a of the reactor and the outlet being provided either at the first end 12a or at least closer to the first end 12 than the second end 12b of the reactor, there will be flows in both directions through the treatment chamber 4. And thanks to the inlet 5a being provided closer to the sleeve 8 than the outlet 5b is the fluid will first flow along the sleeve 8 towards the second end 12b of the reactor and then at a larger distance from the sleeve 8 when the flow of fluid has changed direction at the second end 12b of the reactor and is flowing towards the first end 12a of the reactor and the outlet 5b.

The outlet 5b is hereby provided closer to the outer surrounding wall 12c of the reactor 12 than the inlet 5a is, whereby, when a fluid is transferred through the fluid treatment system for being treated, the fluid will enter the reactor closer to the outer surface 10 of the sleeve 8 than to the outer surrounding wall 12c of the reactor 12 and a return flow through the reactor will mostly be provided closer to the inner surface 14 of the outer surrounding wall

least partly along the sleeve 8 towards the second end 12b of the reactor 12 where it will change direction and flow towards the first end 12a of the reactor for being expelled through the outlet 5b. In Figure 2a the flow of fluid is illustrated by arrows. There will be a part of the flow towards the outlet 5b which will be drawn back into the opposite flow towards the second end 12b of the reactor 12. This is illustrated by the bent arrows in Figure 2a and is a consequence of the higher flow rate at the inlet 5a and pressure difference which will be further described below.

The inlet 5a is suitably provided as an essentially annular inlet around the sleeve 8. Essentially annular would include smaller deviations from a strictly annular form, such as a polygon form or a non-regular annular form. The annular inlet 5a can be provided directly around the sleeve 8 as in the embodiment shown in Figures 1-3 which can be seen in Figures lb and Ic. The inlet 5a can be an annular opening into the treatment chamber 4. However, in another embodiment it can instead be a number of openings arranged in an essentially circular shape around the lamp axis, A. The inlet 5a should be sized to provide a suitable jet flow of the fluid which is entering the treatment chamber 4. To accomplish a jet flow the size of the inlet needs to be comparatively small in relation to a radius of the treatment chamber 4. This is further discussed below.

A size of the inlet 5a can be adapted such that an inlet flow rate of fluid entering the treatment chamber 4 for being treated is higher than a reversed flow rate of the fluid within the treatment chamber 4. Hereby a suitable distribution of flow through the treatment chamber 4 can be provided and upheld whereby an efficient UV treatment can be provided.

The outlet 5b can in some embodiments be provided as an essentially annular outlet around the inlet 5a as shown in the embodiment of Figures 1-3. Essentially annular would include smaller deviations from a strictly annular form, such as a polygon form or a nonregular annular form. The annular outlet 5b can be provided anywhere between the annular inlet 5a and the outer surrounding wall 12c of the reactor 12. If the fluid from the outlet is collected on one side of the fluid treatment system as illustrated in the embodiment as shown in Figures 1-3, it may be suitable to dimension a size of the outlet as a cross sectional area reduction (a pressure loss), such that the fluid is distributed around the whole circumference. Otherwise, the flow distribution within the treatment chamber may be uneven. A smaller sized outlet can improve fluid distribution. However, in another embodiment the outlet 5b can instead be provided as a number of openings arranged in an essentially circular shape around the lamp axis, A. In still another embodiment the outlet could be provided as a number of openings through the surrounding wall 12c of the reactor 12. The position of these openings should be closer to the first end 12a than the second end 12b and a collection device needs to be provided to collect the expelled treated fluid.

A cross section area of the inlet 5a in a perpendicular direction to axis A, can suitably be smaller than 1/3 of a cross section area of the treatment chamber 4 in a perpendicular direction to axis A, such that a flow rate of fluid is higher at the inlet 5a than in the rest of the treatment chamber 4. In some embodiments of the invention a cross section area of the inlet 5a in a perpendicular direction to axis A, is smaller than 1/4 of a cross section area of the treatment chamber 4 in a perpendicular direction to axis A. Hereby the fluid flow rate at the inlet 5a is comparatively high compared to a flow rate of the return flow in the treatment chamber 4. The fluid will hereby flow close along the sleeve 8 toward the second end 12b of the reactor where it will change direction. The flows are illustrated in Figure 2a where it can be seen that without any internal separating walls the flows are kept almost intact.

Hereby the flow passes first through the radiated zone with the highest UV intensity closest to the lamp. Thanks to the high flow rate in the jet flow from the inlet towards the second end of the reactor there is also a strong turbulent mixing within this flow closest to the sleeve. The turbulent mixing assures that all parts of the flow will come closest to the sleeve where the UV intensity is highest and a good efficiency of UV treatment is achieved, i.e. there is a diffusion or transport of fluid within the flow in a perpendicular direction to the flow direction and hereby all fluid will at some point during treatment be exposed to the highest UV intensity closest to the sleeve.

The second end 12b of the reactor 12 is suitably designed for guiding a flow of a fluid being treated in the fluid treatment system 2 to change direction and flow back towards the first end 12a of the reactor mostly at a larger distance from the sleeve 8 than when the fluid arrived at the second end. In some embodiments of the invention, as for example shown in Figures 1-3, the second end 12b of the reactor 12 comprises a concave inner surface 32 for guiding the fluid towards the inner surface 14 of the outer surrounding wall 12c of the reactor 12 when the fluid is changing direction at the second end 12b of the reactor 12. The concave inner surface 32 can in some examples be essentially in the form of a half of a torus. Such a form of a half of a torus is shown in Figures 1-2. Essentially half of a torus would include smaller deviations from such a form. In Figure 3 a slightly different form of the second end 12b of the reactor 12 is shown. Here the concave inner surface 32 comprises a flat bottom part 32a, and one or more radiuses 32b.

With such a design of the second end 12b of the reactor 12 there will be an inversion of the flow when turning back towards the first end 12a, i.e. the fluid which is flowing closest to the sleeve (in a high UV intensity zone) on the way towards the second end 12b will flow closest to the inner surface 14 of the reactor 12 (in a low UV intensity zone) on the other way back towards the first end 12a. Consequently, a part of the flow which on the way towards the second end 12b of the reactor is not flowing closest to the sleeve 8 but further out from the sleeve in a medium-high UV intensity zone will on the way back towards the first end 12a flow a bit further from the sleeve 8, but not all the way out at the inner surface 14 of the reactor 12 and will hereby flow in a medium -low UV intensity zone. This will improve UV treatment efficiency because the UV treatment will be more evenly distributed to all the fluid. This inversion of flow is illustrated in Figure 2a.

A diameter of the fluid treatment chamber 4 can in some embodiments suitably be between 1/3 and 3/1 of an arc length of the ultra-violet (UV) light treatment lamp 6. A smaller reactor diameter than approximately 1/3 of the arc length of the UV lamp would make the desired flow pattern (the double directed flow) to collapse and a larger reactor diameter than approximately 3/1 of the arc length of the UV lamp would not be suitable since the large distance from the lamp would result in such a low UV-light intensity.

For the fluid treatment system 2 according to the invention a flow rate at the inlet 5a can suitably be between 1 m/s and 7 m/s. With such a flow rate the desired flow pattern is achieved, and an efficient UV disinfection with an acceptable pressure drop is provided. The flow rate of the flow coming from the inlet 5a is higher than the flow rate of the flow towards the outlet 5b. The higher flow rate imply a higher dynamic pressure and thereby a lower static pressure. Hence the static pressure is always lower in the flow coming from the inlet 5a than the static pressure of the flow towards the outlet 5b. The lower static pressure drives a flow from the flow towards the outlet 5b to the flow coming from the inlet 5a and hinders a short cutting flow in the opposite direction. This is illustrated by the small bent arrows in Figure 2a.

The illustrated embodiment is only one example. Some of the details, such as for example form and size of different parts can be varied within the scope of the invention. For example, a system inlet 2a and a system outlet 2b of the fluid treatment system 2 can be designed in another way than shown in Figures 1-3. Dimensions can be varied within certain ranges as discussed above. The reactor 12 of the fluid treatment system 2 can have an essentially circular inner cross section but the inner cross section may also deviate somewhat from circular. An outer form of the reactor 12 can of course be varied. The second end 12b of the reactor can have an inner concave surface, for example in the form of a half of a torus as shown in Figures 1-2. However, another form of an inner surface of the second end 12b can also be provided, as discussed above. Furthermore, the inlet 5a and the outlet 5b of the treatment chamber 4 can be dimensioned and positioned differently as discussed above.

Figure 2b shows a CFD (Computational Fluid Dynamics) simulation of the flow pattern in a fluid treatment system according to one embodiment of the invention (as for example the fluid treatment system 2 as shown in Figures 1-3). The arrows show the direction of the fluid velocity. Here it can be seen that without any separating internal walls in the reactor 4 most of the flow will change direction at the second end 12b of the reactor and all incoming fluid will be treated in a high UV intensity zone close to the sleeve on its way from the inlet towards the second end of the reactor. It can be seen that a flow through the reactor which is beneficial for an even UV treatment of the fluid is maintained thanks to the jet flow of the incoming fluid. State-of-the-art CFD simulation shows that one standard execution of the proposed design is approximately 10% more efficient than any optimally sized conventional reactor in the transmittance range 50-90%.

Claims

1. A fluid treatment system (2) comprising: at least one ultra-violet, UV, light treatment lamp (6) arranged within an elongated protective UV-transparent sleeve (8) provided along a central longitudinal axis A, said sleeve (8) having an outer surface (10) and an essentially circular cross- sectional shape; and a reactor (12) configured to receive said sleeve (8), whereby a fluid treatment chamber (4) for receiving fluid to be treated, is provided between an inner surface (14) of the reactor (12) and the outer surface (10) of the sleeve (8), said reactor (12) extending along the axis A, between a first end (12a) and a second end (12b) of the reactor and said treatment chamber (4) comprising an inlet (5a) for receiving fluid to be treated inside the treatment chamber (4) and an outlet (5b) for expelling treated fluid out from the treatment chamber (4), whereby the inlet (5a) is positioned such that fluid is introduced into the treatment chamber (4) from the first end (12a) of the reactor (12) and the outlet (5b) is provided closer to the first end (12a) than to the second end (12b) of the reactor (12), and the inlet (5a) is provided closer to the sleeve (8) than the outlet (5b) is, wherein the treatment chamber (4) is one single open treatment chamber (4) which is surrounding the sleeve (8).

2. Fluid treatment system according to claim 1, wherein the reactor (12) is configured such that when a fluid is transferred as a flow of fluid through the fluid treatment system (2) for being treated, most of the flow of the fluid will change direction at the second end (12b) of the reactor whereby there will be a flow of fluid in both directions between the first and second ends (12a, b) of the reactor (12) within the single open treatment chamber (4).

3. Fluid treatment system according to claim 1 or 2, wherein the outlet (5b) is positioned such that fluid is expelled out from the treatment chamber at the first end (12a) of the reactor. Fluid treatment system according to any one of the claims, wherein the inlet (5a) is provided as an essentially annular inlet around the sleeve (8) or as a number of openings arranged in an essentially circular shape around the lamp axis A. Fluid treatment system according to any one of the preceding claims, wherein a size of the inlet (5a) is adapted such that an inlet flow rate of fluid entering the treatment chamber (4) for being treated is higher than a reversed flow rate of the fluid within the treatment chamber (4). Fluid treatment system according to any one of the preceding claims, wherein the outlet (5b) is provided as an essentially annular outlet around the inlet (5a) or as a number of openings arranged in an essentially circular shape around the lamp axis A. Fluid treatment system according to any one of the preceding claims, wherein a cross section area of the inlet (5a) in a perpendicular direction to axis A, is smaller than 1/3 of a cross section area of the treatment chamber (4) in a perpendicular direction to axis A, such that a flow rate of fluid is higher at the inlet than in the rest of the treatment chamber (4). Fluid treatment system according to any one of the preceding claims, wherein the second end (12b) of the reactor is designed for guiding a flow of a fluid being treated in the fluid treatment system to change direction and flow back towards the first end (12a) of the reactor mostly at a larger distance from the sleeve (8) than when the fluid arrived at the second end. Fluid treatment system according to any one of the preceding claims, wherein the second end (12b) of the reactor (12) comprises a concave inner surface. Fluid treatment system according to any one of the preceding claims, wherein a diameter of the fluid treatment chamber (4) is between 1/3 and 3/1 of an arc length of the ultra-violet (UV) light treatment lamp (6).